Mile-wide tornado smashes Windsor, Colorado; plus, hurricane season commentary

By: Dr. Jeff Masters , 1:23 PM GMT on May 23, 2008

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A mile-wide tornado swept through Colorado between 11am and noon yesterday, ripping the roofs off buildings, tossing cars into the air, and killing at least one person in Weld County, northeast of Denver. Hail up to 2.75" in diameter accompanied the storm, which took an unusual north-northwesterly track , parallel to the Rocky Mountains north of Denver. Hardest hit was the town of Windsor, between Fort Collins and Greely, where damage appeared to be at least EF3. A local TV station took some impressive live video of the tornado, and a wunderground web cam video in Windsor, Colorado (Figure 1) caught the funnel as it passed east of the camera.


Figure 1.Webcam view looking east at 11:45am MDT in Windsor, Colorado as the tornado passed by. Note the golf ball-sized hail covering the ground. Image credit: windsorweather.com.

The Weather Underground's tornado expert, Rob Carver, had this explanation of yesterday's tornadoes:

Two low pressure systems over the Western U.S. were the cause of the severe weather outbreak of May 22. A strong upper-level low over the Great Basin formed a surface low in the lee of the Rockies, and brought a strong southerly mid-level jet over the Plains of Colorado and Kansas. As the surface low formed, it brought warm moist air northwards, forming a warm front. This warm air moved westward, rising with the terrain, causing thunderstorms to form. Once these storms formed, the juxtaposition of easterly flow at the surface with southerly flow aloft (i.e., wind shear) produced significant spin in the horizontal direction, which was tilted by the storms to vertical spin, which triggered the formation of tornadic thunderstorms. This movement of the warm front up the slope of the Rockies to help trigger tornadic thunderstorms is a rare occurrence.



Figure 2. Radar reflectivity image (top) of the Windsor, Colorado tornado at 11:45am MDT May 22, 2008. Note the classic hook-shaped echo associated with the tornado. Bottom: Doppler velocity image of the tornado, showing a small core of red and blue colors right next to each other, denoting strong winds towards and away from the radar, the classic signature of a tornado vortex. For those interested, we've saved an animation of the reflectivity and Doppler velocity.

Severe weather forecast
Severe weather is expected today over Kansas, Nebraska, and surrounding states. NOAA's Storm Prediction Center has placed portions of this area under its "Moderate Risk" category for severe weather, one step below its highest level of concern, "High Risk". Yesterday was also a "Moderate Risk" day, which SPC later upgraded to "High Risk" once the tornadoes started pounding Colorado. More severe weather is expected Saturday and Sunday over the Midwest as the upper-level low pressure system responsible moves slowly eastward. The Weather Underground Severe Weather page and Tornado page and WebCam page are good places to go to follow the severe weather. Also, tune in to the chase accounts and awesome storm photos from Wunderblogger Mike Theiss, who was in Kansas yesterday, and has posted many spectacular photos of yesterday's storms. According to Mike's blog:

Today Cloud 9 Tours saw 4 tornadoes and ONE developing almost overhead. We experienced winds over 100mph from the circulation of the meso that passed overhead as a cone tornado developed. Stay Tuned....


Possible development in the Eastern Pacific late next week
The past four days, the ECMWF model has been predicting the formation of a tropical storm in the the Eastern Pacific, just off the coast of Guatemala, around May 29. The GFS model has also been predicting something might develop, but in the Western Caribbean near Mexico's Yucatan Peninsula. The GFS has been rather inconsistent with its handling of this potential storm, and I am inclined to discount its forecast--especially since last night's long range runs of the NOGAPS, Canadian, and UKMET models all show development in the Eastern Pacific, not the Caribbean. All five models predict a northward shift in the jet stream and substantial relaxation in wind shear over the Eastern Pacific and Western Caribbean next week. It is common to see May tropical storms in the Eastern Pacific, and it would not be a surprise to see something develop there. I'd put the odds of something popping up in the Western Caribbean or Gulf of Mexico at less than 10%, though.

NOAA's seasonal hurricane forecast
NOAA issued its annual seasonal hurricane forecast yesterday, which I discussed in detail in yesterday's blog entry. Yesterday's forecast came out with a little more uncertainty attached to it than previous forecasts, which is a good thing. The media attention and fanfare that accompanies these forecasts is rather excessive, given the low skill they have. In fact, we don't even know if the NOAA forecasts have ANY mathematical skill, because they've never released a verification study of their forecasts. I doubt that the skill is very high--as Eric Berger of the Houston Chronicle pointed out in a blog yesterday, NOAA has blown its forecast of Accumulated Cyclone Energy (ACE) each of the last six years. NOAA held its usual press conference to announce the forecast; this year, it was held at the home of the NOAA Hurricane Hunter aircraft, MacDill AFB in Tampa. The NOAA dignitaries present said all the right things, preaching the need for preparedness regardless of the forecast for the upcoming hurricane season. Still, I wonder if NOAA might be hurting themselves by making such a public spectacle over the release of a forecast that no one knows the accuracy of, and has performed poorly by some measures in recent years. I do like the fact they are issuing public hurricane forecasts, as I expect their accuracy and value will improve in coming years, but they're definitely not worth the attention they're getting at present.

Jeff Masters

Tornado1 (kd7tda)
One of several tornados. This one was near Grainfield, KS
Tornado1
Tornado Damage 3 (jlg)
Damage from today's Tornado in Windsor, Colorado
Tornado Damage 3
()
Mean Looking Meso with Cone Tornado (MikeTheiss)
Photo os a wallcloud with a developing tornado passing just to the north of our location on May 22nd, 2008. Photo copyright Mike Theiss
Mean Looking Meso with Cone Tornado

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1207. Midweststorm
8:51 PM GMT on May 24, 2008
Ive been watching since the 2nd 'nado dropped. this storm continually creates new hook echos and they build fast and strong
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1206. weathersp
4:50 PM EDT on May 24, 2008
It seems like this storm doesn't know where to put its COC.. LOL

2 wall clouds and 4 tornados?
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1205. SouthDadeFish
8:48 PM GMT on May 24, 2008
Its amazing how fast they appear and how fast they go right back up. This is why it's always better to error on the side of caution. I hope everyone in this area is taking cover.
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1204. zoomiami
8:50 PM GMT on May 24, 2008
Thats what I thought - it looks almost even with the ground.
Member Since: August 13, 2007 Posts: 10 Comments: 4158
1203. nash28
8:50 PM GMT on May 24, 2008
Good lord! That new wall cloud is basically on the ground!
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1202. nash28
8:48 PM GMT on May 24, 2008
Tornado gone.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1201. nash28
8:48 PM GMT on May 24, 2008
Going back up...
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1200. nash28
8:46 PM GMT on May 24, 2008
It's on the ground.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1199. nash28
8:46 PM GMT on May 24, 2008
#4 forming. Almost down.
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1198. weathersp
8:44 PM GMT on May 24, 2008
Those are some big vortices.. I thought they were small tornados..
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1197. nash28
8:43 PM GMT on May 24, 2008
Figures...

The second I said that, the guy in the chopper said it:-)
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1196. FLWeatherFreak91
8:43 PM GMT on May 24, 2008
radar just indicated rotation again!
Member Since: December 1, 2006 Posts: 2 Comments: 3634
1195. nash28
8:43 PM GMT on May 24, 2008
Looks to be back building.

Member Since: July 11, 2005 Posts: 190 Comments: 16972
1194. FLWeatherFreak91
8:42 PM GMT on May 24, 2008
I'm watching the radar for the tornado as well as the vid and if another tornado comes down it should be over fields. I don't see any towns in its path on google earth
Member Since: December 1, 2006 Posts: 2 Comments: 3634
1193. nash28
8:41 PM GMT on May 24, 2008
That is one large wall cloud. Just can't get its act together enough yet.....
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1192. zoomiami
8:40 PM GMT on May 24, 2008
does anyone know where the helicopter crew are from? Are they storm chasers?
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1191. nash28
8:37 PM GMT on May 24, 2008
Wall cloud and multiple vorticies getting rain wrapped.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1190. nash28
8:33 PM GMT on May 24, 2008
Yep. Giant wall cloud. The right side has great rotation. Funnel will be coming soon I imagine.
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1189. stormlvr
8:31 PM GMT on May 24, 2008
To my fellow weather "nuts". Just took a quick look at the 12z operational GFS with regards to potential movement of the potential system in the gulf LOL. Initially the disturbance should be driven by the low level flow with a gentle tug to the north exerted by a trof to the north. Development would give increasing influence to the trof as depicted by the GFS. One of the problems I have seen with the GFS is giving to much influence to trofs and for to long. Even the GfS in the longer range allows the trof to pass east with ridging pushing the system from Central Fl west across the northern Gulf before a second trof picks it up. I'm not so sure I would completely discount a westward movement with this system especially if the GFS is overplaying the influence of the first trof and it ends up further south.
Member Since: August 12, 2007 Posts: 0 Comments: 323
1188. weathersp
8:30 PM GMT on May 24, 2008
For anyone watching the Tornado..

You see that whole wall cloud rotating.. holy cow.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1187. Michfan
8:29 PM GMT on May 24, 2008
Afternoon all. Skies look like we might get some Thunderboomers this evening around Pcola. Any updates on the waves we were watching and the GFS spawning that storm near Panama?
Member Since: September 7, 2007 Posts: 0 Comments: 1738
1186. KrazyKaneLove
8:21 PM GMT on May 24, 2008
heli in a tornado..be kinda like a hummingbird in a hurricane.. I really hope Memorial Day weekend will be a happy one w/out any major natural disasters..
Member Since: September 7, 2007 Posts: 0 Comments: 429
1185. HadesGodWyvern (Mod)
8:19 PM GMT on May 24, 2008
MET OFFICE TROPICAL CYCLONE GUIDANCE FOR NORTH-EAST PACIFIC


GLOBAL MODEL DATA TIME 12UTC 24.05.2008



NEW TROPICAL STORM FORECAST TO DEVELOP AFTER 48 HOURS
FORECAST POSITION AT T 48 : 9.6N 94.8W

VERIFYING TIME POSITION STRENGTH TENDENCY
-------------- -------- -------- --------
12UTC 26.05.2008 9.6N 94.8W WEAK
00UTC 27.05.2008 8.7N 92.5W WEAK INTENSIFYING SLIGHTLY
12UTC 27.05.2008 8.4N 90.3W MODERATE INTENSIFYING RAPIDLY
00UTC 28.05.2008 8.9N 89.1W MODERATE INTENSIFYING SLIGHTLY
12UTC 28.05.2008 9.6N 89.2W STRONG LITTLE CHANGE
00UTC 29.05.2008 10.4N 90.1W STRONG LITTLE CHANGE
12UTC 29.05.2008 10.8N 91.0W INTENSE INTENSIFYING RAPIDLY
00UTC 30.05.2008 11.3N 91.5W INTENSE INTENSIFYING SLIGHTLY
12UTC 30.05.2008 11.9N 91.6W INTENSE INTENSIFYING RAPIDLY


THIS INFORMATION IS PROVIDED AS GUIDANCE FOR TROPICAL CYCLONE RSMCS.

IT REQUIRES INTERPRETATION BY TROPICAL CYCLONE SPECIALISTS AND SHOULD NOT BE CONSIDERED AS A FINAL PRODUCT MET OFFICE, EXETER, UK
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1184. nash28
8:18 PM GMT on May 24, 2008
Man!!! That is one VERY BLACK wall cloud!
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1183. 1900hurricane
8:17 PM GMT on May 24, 2008
Man, that storm's got quite a wall cloud. That would be so terrible if it were all to drop and form a giant wedge.....
Member Since: August 2, 2006 Posts: 47 Comments: 11690
1182. msphar
8:17 PM GMT on May 24, 2008
Glad to see all's quiet on the Southeastern front, please try to keep it this way and keep those models the heck out of the MDR.
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1181. weathersp
8:11 PM GMT on May 24, 2008
Aww this is so cool.. Vorticies on the ground..

Link
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1180. hurricane23
8:05 PM GMT on May 24, 2008
.
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1179. hahaguy
8:01 PM GMT on May 24, 2008
got a small cell almost by me in psl raining hard and very windy
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1178. smmcdavid
7:59 PM GMT on May 24, 2008
Unbelievable Terra...

Afternoon all.
Member Since: September 20, 2005 Posts: 31 Comments: 2309
1177. KrazyKaneLove
7:58 PM GMT on May 24, 2008
well, I'm off to work on this fine memorial day weekend, but actually looking forward to the high powered AC that my dining establishment provides...stay cool y'all..bbl
Member Since: September 7, 2007 Posts: 0 Comments: 429
1175. weathersp
7:54 PM GMT on May 24, 2008
Helicopter has got a Tornado in Oklahoma live..

Video Feed

Radar
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1174. moonlightcowboy
7:53 PM GMT on May 24, 2008


Very little dry air/dust in the cATL.



Plenty of dry air in the Carib and GOM. SSTs and TCHP should start popping.



Very little shear in the Carib and GOM.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1173. TerraNova
7:53 PM GMT on May 24, 2008
LIVE CNN/KWTV coverage of tornado.
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1172. HurricaneGeek
7:49 PM GMT on May 24, 2008
96.3 °F

seflagamma, I'm almost there. =)
In West Palm
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1171. weathergeek5
7:48 PM GMT on May 24, 2008
WATCH CNN LIVE COVERAGE OF A POWERFUL TORNADO
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1170. hurricane23
7:48 PM GMT on May 24, 2008
FLORIDA RADARS PAGE

Member Since: May 14, 2006 Posts: 8 Comments: 13841
1169. seflagamma
7:46 PM GMT on May 24, 2008
Oh yes, we've had about 7 record breaking days in Dade and Broward so far in May this year and been in mid 90's almost everyday. That is unheard of for May! Makes me wonder what is in store for us later...
Member Since: August 29, 2005 Posts: 301 Comments: 40944
1168. FLWeatherFreak91
7:46 PM GMT on May 24, 2008
It's hot in Tampa, but unfortunately the seabreeze has already gone WAY inland sp we don't have a chance for rain anymore... This west wind is stealing our rain and giving it away to the east.... merry Christmas
Member Since: December 1, 2006 Posts: 2 Comments: 3634
1166. KrazyKaneLove
7:43 PM GMT on May 24, 2008
gamma , that was me in western palm beach with a temp of 99.7! I think it is accurate too as my house temp is now 86 with the AC on full blast..no one is really talking about the extreme heat for this time of year.
Member Since: September 7, 2007 Posts: 0 Comments: 429
1165. 1900hurricane
7:42 PM GMT on May 24, 2008
I win.

Greengate Subdivision, Spring, Texas (PWS)
Updated: 14 sec ago
99.1 °F / 37.3 °C
Scattered Clouds
Humidity: 53%
Dew Point: 79 °F / 26 °C
Wind: 2.0 mph / 3 km/hfrom the SE
Wind Gust: 24.3 mph / 39 km/h
Pressure: 29.90 in / 1012.4 hPa (Falling)
Heat Index: 119 °F / 48 °C
Member Since: August 2, 2006 Posts: 47 Comments: 11690
1163. Drakoen
7:37 PM GMT on May 24, 2008
1160. hurricane23 7:31 PM GMT on May 24, 2008
Drak take a look at THIS and loop it.I use it sometimes for probability of TC.


I'm wondering whats that even based on.
Member Since: October 28, 2006 Posts: 57 Comments: 30670
1162. weathers4me
7:36 PM GMT on May 24, 2008
WOW. CHeck out CNN!! Just caught a tornado live in OK. Amazing footage..
Member Since: May 24, 2007 Posts: 0 Comments: 118
1161. seflagamma
7:36 PM GMT on May 24, 2008
someone post a high 90's temp earlier and ask can anyone top that.. well here in central Broward County.. here is current conditions.

Near the Glades, Southwest Ranches, Florida (PWS)
Updated: 9 sec ago
97.2 °F / 36.2 °C
Partly Cloudy
Humidity: 37%
Dew Point: 67 °F / 19 °C
Wind: 8.1 mph / 13 km/hfrom the SW
Wind Gust: 8.1 mph / 13 km/h
Pressure: 29.88 in / 1011.7 hPa (Falling)
Heat Index: 101 °F / 39 °C

That low humidity of 37% is strange; we just don't get that low of humidity around here. It is always hot and humid not hot and dry ...but as I said yesterday for past few weeks it has been hot and dry. With these temps whent those afternoon TS do pop up with will have plenty of fuel.

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1160. hurricane23
7:31 PM GMT on May 24, 2008
Drak take a look at THIS and loop it.I use it sometimes for probability of TC.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
1159. Drakoen
7:34 PM GMT on May 24, 2008
HPC showing that closed area of low pressure by Honduras on Saturday.
Photobucket
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1158. moonlightcowboy
7:30 PM GMT on May 24, 2008


Sfc map shows the twave running considerably higher out at 45w. The ePac low stationary and the low off the FL coast moving n thru 72 hrs.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1157. BoynSea
7:26 PM GMT on May 24, 2008
1152. hurricane23 7:21 PM GMT on May 24, 2008

Thank you.
Member Since: October 8, 2007 Posts: 0 Comments: 87

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.